Titanium dioxide pigments are used in a wide variety of applications such as in paints, plastics, paper, laminates, siding, corrosion resistant primers, decorative topcoats, or other coating systems. In general, the titanium dioxide pigments used in these applications are either in anatase or rutile form and made by well-known processes such as the sulfate or chloride process.
In the sulfate process, ore-containing titanium is reacted with sulfuric acid and titanium is obtained by selective precipitation, washing, followed by calcination of the titanium hydrate to form anatase or rutile titanium dioxide. The chloride process involves reacting ore containing titanium with chlorine to produce titanium tetrachloride, which is then purified and oxidized to form titanium dioxide, usually in rutile form.
The anatase or rutile titanium dioxide may be further processed, for example, by treating the titanium dioxide (TiO2) with inorganic compounds such as, for example, alumina, phosphate, zirconia, and silica to enhance properties of the pigment. For plastics applications, the titanium dioxide may be further treated with organic compounds to make the TiO2 hydrophobic for introduction into the particular plastics system.
Numerous hydrophobic agents, for example, polyols, phosphorylated fatty acid derivatives, organophosphates, dialkylsulfosuccinates and various silicone-based agents have been used to make TiO2 hydrophobic. Some silicone-based agents used for making the TiO2 hydrophobic include silanes, siloxanes, polysiloxanes and substituted silanes, hydrosylates and condensates of these silanes, siloxanes and polysiloxanes agents.
The hydrophobic agent may be added to the TiO2 when it is in the wet or dry phase to give TiO2 the desired performance. In the wet phase, the hydrophobic agent can be applied to a slurry of TiO2, with agitation and allowed to age for a certain length of time before the pigment is washed, dried and micronized. Alternatively, in the wet phase, the hydrophobic agent can be applied directly to the filter cake or spray dryer feed slurry before drying and micronizing. When the titanium dioxide pigment is in the dry phase, e.g., without any solvent present, the hydrophobic agent may be sprayed onto the dry TiO2 particle surface at the micronization stage.
Unfortunately, some of the hydrophobic agents have certain disadvantages. For example, some hydrophobic agents require that the TiO2 surface is first treated with inorganic compounds, such as alumina, in order to facilitate the attachment of the hydrophobic agent onto the TiO2 surface. Some hydrophobic agents can only be applied to the TiO2 solely when the TiO2 is in the wet phase or solely when it is in the dry phase. Some hydrophobic agents are not suitable for high temperature applications because they do not form a strong bond with the TiO2 surface and migrate from the surface of the pigment leading to potential problems with heat sealing, print clarity and other related problems in the final pigmented product.
Because of the disadvantages mentioned above, there is a need for new titanium dioxide pigments and methods for producing commercially acceptable titanium dioxide pigments at high throughput rates that have improved lacing resistance, dispersibility, stability or combination thereof.